The partial British military withdrawal from southern Iraq announced by Tony Blair this week follows political and military failure, and is not because of any improvement in local security, say specialists on Iraq.

In a comment entitled "The British Defeat in Iraq" the pre-eminent American analyst on Iraq, Anthony Cordesman of the Centre for Strategic and International Studies, in Washington, asserts that British forces lost control of the situation in and around Basra by the second half of 2005.

Mr Cordesman says that while the British won some tactical clashes in Basra and Maysan province in 2004, that "did not stop Islamists from taking more local political power and controlling security at the neighbourhood level when British troops were not present". As a result, southern Iraq has, in effect, long been under the control of the Supreme Council for Islamic Revolution in Iraq (Sciri) and the so-called "Sadrist" factions.

Mr Blair said for three years Britain had worked to create, train and equip Iraqi Security Forces capable of taking on the security of the country themselves. But Mr Cordesman concludes: "The Iraqi forces that Britain helped create in the area were little more than an extension of Shia Islamist control by other means."

The British control of southern Iraq was precarious from the beginning. Its forces had neither experience of the areas in which they were operating nor reliable local allies. Like the Americans in Baghdad, they failed to stop the mass looting of Basra on the fall of Saddam Hussein and never established law and order.

American and British officials never appeared to take on board the unpopularity of the occupation among Shia as well as Sunni Iraqis. Mr Blair even denies that the occupation was unpopular or a cause of armed resistance. But from the fall of Saddam Hussein, mounting anger against it provided an environment in which bigoted Sunni insurgents and often criminal Shia militias could flourish.